```html
<!DOCTYPE html>
<html lang="zh-CN">
<head>
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    <title>环形链表算法解析</title>
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</head>
<body>
    <div class="min-h-screen">
        <!-- Hero Section -->
        <section class="hero-gradient text-white py-20 md:py-32 px-4 md:px-0">
            <div class="container mx-auto max-w-5xl text-center">
                <h1 class="text-4xl md:text-6xl font-bold mb-6 tracking-tight">环形链表检测</h1>
                <p class="text-xl md:text-2xl font-light mb-8 max-w-3xl mx-auto leading-relaxed">
                    探索快慢指针算法在链表环检测中的精妙应用
                </p>
                <div class="flex justify-center space-x-4">
                    <span class="px-4 py-2 bg-white text-indigo-600 rounded-full font-medium">#算法</span>
                    <span class="px-4 py-2 bg-white text-indigo-600 rounded-full font-medium">#数据结构</span>
                    <span class="px-4 py-2 bg-white text-indigo-600 rounded-full font-medium">#LeetCode</span>
                </div>
            </div>
        </section>

        <!-- Main Content -->
        <section class="container mx-auto max-w-5xl px-4 md:px-0 py-12 md:py-20">
            <!-- Problem Section -->
            <div class="bg-white rounded-xl shadow-lg p-8 mb-12 card-hover">
                <div class="flex items-center mb-6">
                    <div class="w-10 h-10 rounded-full bg-indigo-100 flex items-center justify-center mr-4">
                        <i class="fas fa-question text-indigo-600"></i>
                    </div>
                    <h2 class="text-2xl md:text-3xl font-bold text-gray-800">题目描述</h2>
                </div>
                <p class="text-gray-700 leading-relaxed mb-6">
                    给定一个链表，判断链表中是否有环。如果链表中存在环，则返回 <span class="font-mono bg-gray-100 px-2 py-1 rounded">true</span>；否则，返回 <span class="font-mono bg-gray-100 px-2 py-1 rounded">false</span>。
                </p>
                <p class="text-gray-700 leading-relaxed">
                    环是指链表的尾部连接到链表中的某个位置（不一定是头部）。
                </p>
            </div>

            <!-- Solution Section -->
            <div class="grid md:grid-cols-2 gap-8 mb-12">
                <!-- Fast-Slow Pointer -->
                <div class="bg-white rounded-xl shadow-lg p-8 card-hover">
                    <div class="flex items-center mb-6">
                        <div class="w-10 h-10 rounded-full bg-purple-100 flex items-center justify-center mr-4">
                            <i class="fas fa-tachometer-alt text-purple-600"></i>
                        </div>
                        <h2 class="text-2xl font-bold text-gray-800">快慢指针法</h2>
                    </div>
                    <p class="text-gray-700 leading-relaxed mb-6">
                        使用快慢指针，快指针每次走两步，慢指针走一步。若存在环，两指针必相遇。
                    </p>
                    <div class="space-y-2 mb-6">
                        <div class="flex items-start">
                            <div class="w-5 h-5 rounded-full bg-purple-100 flex-shrink-0 flex items-center justify-center mr-3 mt-1">
                                <i class="fas fa-check text-purple-600 text-xs"></i>
                            </div>
                            <p class="text-gray-700">时间复杂度: O(n)</p>
                        </div>
                        <div class="flex items-start">
                            <div class="w-5 h-5 rounded-full bg-purple-100 flex-shrink-0 flex items-center justify-center mr-3 mt-1">
                                <i class="fas fa-check text-purple-600 text-xs"></i>
                            </div>
                            <p class="text-gray-700">空间复杂度: O(1)</p>
                        </div>
                    </div>
                    <div class="mermaid mb-4">
                        graph LR
                        A[初始化慢指针slow, 快指针fast] --> B{fast和fast.next不为空?}
                        B -->|是| C[slow前进一步]
                        C --> D[fast前进两步]
                        D --> E{slow == fast?}
                        E -->|是| F[检测到环, 返回true]
                        E -->|否| B
                        B -->|否| G[未检测到环, 返回false]
                    </div>
                </div>

                <!-- Hash Table -->
                <div class="bg-white rounded-xl shadow-lg p-8 card-hover">
                    <div class="flex items-center mb-6">
                        <div class="w-10 h-10 rounded-full bg-blue-100 flex items-center justify-center mr-4">
                            <i class="fas fa-history text-blue-600"></i>
                        </div>
                        <h2 class="text-2xl font-bold text-gray-800">哈希表法</h2>
                    </div>
                    <p class="text-gray-700 leading-relaxed mb-6">
                        记录访问过的节点，若重复访问则有环。
                    </p>
                    <div class="space-y-2 mb-6">
                        <div class="flex items-start">
                            <div class="w-5 h-5 rounded-full bg-blue-100 flex-shrink-0 flex items-center justify-center mr-3 mt-1">
                                <i class="fas fa-check text-blue-600 text-xs"></i>
                            </div>
                            <p class="text-gray-700">时间复杂度: O(n)</p>
                        </div>
                        <div class="flex items-start">
                            <div class="w-5 h-5 rounded-full bg-blue-100 flex-shrink-0 flex items-center justify-center mr-3 mt-1">
                                <i class="fas fa-check text-blue-600 text-xs"></i>
                            </div>
                            <p class="text-gray-700">空间复杂度: O(n)</p>
                        </div>
                    </div>
                    <div class="mermaid">
                        graph LR
                        A[初始化哈希表visited] --> B{当前节点不为空?}
                        B -->|是| C[节点在visited中?]
                        C -->|是| D[检测到环, 返回true]
                        C -->|否| E[将节点加入visited]
                        E --> F[移动到下一个节点]
                        F --> B
                        B -->|否| G[未检测到环, 返回false]
                    </div>
                </div>
            </div>

            <!-- Code Section -->
            <div class="bg-white rounded-xl shadow-lg overflow-hidden mb-12">
                <div class="flex items-center bg-gray-100 px-6 py-3">
                    <div class="w-3 h-3 rounded-full bg-red-500 mr-2"></div>
                    <div class="w-3 h-3 rounded-full bg-yellow-500 mr-2"></div>
                    <div class="w-3 h-3 rounded-full bg-green-500 mr-2"></div>
                    <span class="text-gray-600 ml-2 font-mono">Solution.java</span>
                </div>
                <div class="p-6 code-block text-gray-300">
                    <pre><code class="language-java">
/**
 * 链表节点定义
 */
public class ListNode {
    int val;
    ListNode next;
    ListNode(int x) {
        val = x;
        next = null;
    }
}

public boolean hasCycle(ListNode head) {
    // 如果链表为空或只有一个节点，则不可能有环
    if (head == null || head.next == null) {
        return false;
    }
    
    // 初始化快慢指针，都指向头节点
    ListNode slow = head;
    ListNode fast = head;
    
    // 快指针每次走两步，慢指针每次走一步
    // 当快指针到达链表末尾时停止
    while (fast != null && fast.next != null) {
        // 慢指针前进一步
        slow = slow.next;
        // 快指针前进两步
        fast = fast.next.next;
        
        // 如果快慢指针相遇，说明链表中存在环
        if (slow == fast) {
            return true;
        }
    }
    
    // 如果快指针到达链表末尾，说明链表中不存在环
    return false;
}
                    </code></pre>
                </div>
            </div>

            <!-- Explanation Section -->
            <div class="bg-white rounded-xl shadow-lg p-8 card-hover">
                <div class="flex items-center mb-6">
                    <div class="w-10 h-10 rounded-full bg-green-100 flex items-center justify-center mr-4">
                        <i class="fas fa-lightbulb text-green-600"></i>
                    </div>
                    <h2 class="text-2xl font-bold text-gray-800">算法解析</h2>
                </div>
                <div class="text-gray-700 leading-relaxed space-y-6">
                    <p>
                        <span class="first-letter">快</span>慢指针算法，也称为Floyd判圈算法，是一种用于检测链表或序列中循环的高效方法。它的核心思想类似于两个人在环形跑道上跑步，速度快的人最终会追上速度慢的人。
                    </p>
                    <p>
                        在链表环检测中，我们设置两个指针：快指针和慢指针。快指针每次移动两步，慢指针每次移动一步。如果链表中存在环，快指针最终会追上慢指针（即两者指向同一个节点），此时可以确定链表有环。
                    </p>
                    <p>
                        为什么快慢指针一定能相遇？因为在环中，快指针相对于慢指针的速度是每次移动一步（快：+2步，慢：+1步）。假设环的长度为L，快指针最多需要L次移动就能追上慢指针。
                    </p>
                    <p>
                        这种方法的优势在于它只需要O(1)的额外空间，是检测链表环的最优解。
                    </p>
                </div>
            </div>
        </section>
    </div>

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```